Arrangement and method for update of configuration cache data

ABSTRACT

An arrangement and method for update of configuration cache data in a disk storage subsystem in which a cache memory ( 110 ) is updated using two-phase ( 220, 250 ) commit technique. 
     This provides the advantage that known changes to the subsystem do not require an invalidate/rebuild style operation on the cache. This is especially important where a change will invalidate the entire cache.

FIELD OF THE INVENTION

This invention relates to data storage systems (and subsystems) and methods for operation thereof.

BACKGROUND OF THE INVENTION

In the field of this invention it is known that enhanced function storage subsystems (e.g., for a system of one or more disk drives) contain many logical resources. These resources can be managed by a storage adapter or controller. In this context, a logical resource is an entity which exposes a disk-like behaviour but which may have properties not ordinarily associated with individual disk drives. These properties include enhanced performance, reliability, availability and data transformation operations such as flash copy. There may be a complex many-to-many relationship between logical resources and other logical resources or physical resources. For example a RAID-5 (Redundant Array of Independent Disks) arrangement contains usually between 4 and 16 component disks. Data is striped across the components and a parity check is calculated and stored. The attributes of, and relationships between, these logical resources must be gathered and manipulated by software products to allow users to maintain their subsystem. Since the primary purpose of such a storage subsystem is to perform Input/Output (IO) operations from operating system to disk drive(s)—IO has priority. This may be at the expense of user transactions that are sent to the subsystem in order to generate the details of the logical resources available in the subsystem. This in turn can result in very slow user response times—especially when the subsystem is under heavy IO load.

It is known to provide a cache of subsystem configuration data. This provides a centralised point of reference for user information relating to the subsystem. It is known from U.S. Pat. No. 5,895,493 that such a system will gather information from various systems and provide a point for the user to access and obtain information about a group of systems.

However, this approach has the disadvantage(s) that the system of the referenced patent does not describe how this data is updated. It relies on the subsystems notifying the main cache of changes and updates and passing the data.

A need therefore exists for an arrangement and method of updating storage subsystem cache data wherein the abovementioned disadvantage(s) may be alleviated.

STATEMENT OF INVENTION

In accordance with a first aspect of the present invention there is provided an arrangement for update of cache data in a storage system, the arrangement comprising: memory means for holding data; cache means for holding data associated with the memory means; means for preparing change data for updating the cache means; means for submitting a request for change to the memory means; means for receiving a signal from the memory means representative of completion of the request for change; and means for updating the cache means with the change data in response to the signal indicating successful completion of the request for change.

Preferably, the data comprises configuration data.

Preferably, the storage system comprises a disk storage subsystem.

Preferably, the memory means is comprised in a disk adapter.

Preferably, the memory means is comprised in a disk controller.

The arrangement preferably further comprises interconnect means coupled between the memory means and the cache means for communicating the request for change, the signal representative of completion of the request for change.

Preferably, the interconnect means is also arranged to communicate transaction data.

Preferably, the the interconnect means comprises a device driver.

According to a second aspect of the present invention, there is provided a method for update of cache data in a storage system, the method comprising: providing memory means holding data; providing cache means holding data associated with the memory means; preparing change data for updating the cache means; submitting a request for change to the memory means;receiving a signal from the memory means representative of completion of the request for change; and updating the cache means with the change data in response to the signal indicating successful completion of the request for change.

Preferably, the data comprises configuration data.

Preferably, the storage system comprises a disk storage subsystem.

Preferably, the memory means is provided in a disk adapter.

Preferably, the memory means is provided in a disk controller.

The method preferably further comprises providing interconnect means coupled between the memory means and the cache means for communicating the request for change, the signal representative of completion of the request for change.

Preferably, the interconnect means also communicates transaction data.

Preferably, the interconnect means comprises a device driver.

In a third aspect, the present invention provides a computer program element comprising computer program means for performing the method of the second aspect, and preferably for performing the additional preferred features of the method of the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

One arrangement and method of updating configuration cache data incorporating the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIGS. 1A and 1B are schematic diagrams showing possible routes for user requests in a disk storage subsystem having a host service routine or agent containing a cache and accessing the storage subsystem via an interconnect;

FIG. 2 shows a flow chart illustrating a write-through cache method with two phase commit used in the system of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT

Enhanced function storage subsystems (e.g., for a system of one or more disk drives) contain many logical resources. Each logical resource generally relates to a particular function, for example a RAID-5 logical resource, a flash copy logical resource, etc. The attributes associated with these logical resources must be gathered by software products to allow users to maintain their subsystem. Since the primary purpose of such a storage subsystem is to perform Input/Output (IO) operations from operating system to disk drive(s)—IO has priority. This may be at the expence of user transactions that are sent to the subsystem in order to generate the details of the logical resources available in the subsystem. This in turn can result in very slow user response times—especially when the subsystem is under heavy IO.

In summary, the preferred embodiment of this invention provides a way in which the configuration software running in the host can cache the results of the logical resource configuration discovery transactions and hence re-use the same transaction data when applicable. The present invention is based on the realisation by the inventor that in general subsystem logical resources do not change, and that therefore the cache can be used in preference to “talking” to the subsystem to find out what it has in terms of logical resources. This results in greatly reduced user response times, and reduces the non-essential workload on the subsystem. In particular the preferred embodiment of this invention provides a method of cache update involving a 2-phase commit of the data.

The configuration cache can be implemented in various ways, the preferred embodiment being illustrated with respect to FIG. 1.

The cache 110 is part of an agent or service 120 that runs in the host that connects to the storage subsystem. This service, when initialised, can request all the logical resource information from the storage subsystem 130 via an interconnect 140 which may be the same interconnect that is used for I/O transactions or may be another interconnect specifically provided for the purposes of configuration. The logical configuration data that is returned is saved in the cache for subsequent use. The storage subsystem also returns a Configuration Version Number (CVN). This number is the current CVN stored (130C) by the storage subsystem, and hence ‘version stamps’ the current configuration cache. The storage subsystem increments this number whenever it detects a change in its logical configuration. In this way the software can ask the storage subsystem its CVN, check this against the CVN (110C) that was stored in the cache and act accordingly.

It will be understood that, although as shown in FIG. 1 communication between the service and the subsystem occurs via the interconnect 140, this interconnect may in practice be provided in the form of a device driver in an adapter-based solution where the device driver communicates with an adapter, as shown in FIG. 1A, of the storage subsystem. Alternatively, the interconnect may communicate with a controller, as shown in FIG. 1B, of the storage subsystem. It will further be understood that the arrangement shown in FIG. 1 represents both “in band” communication where the service uses the same route as I/O transactions and “out of band” communication over perhaps Ethernet or some other interconnect.

For example, where a single host contains an adapter and the required “service” software is running in the host:

-   a) The service requests the entire logical configuration from the     adapter. -   b) The service receives the transaction data (stores it in the     cache) and a CVN=123. -   c) Some time later the service receives a request from one of its     clients that involves generating a “view” of a logical resource. -   d) The service requests the adapter CVN (130C) -   e) The adapter returns a CVN=123 -   f) The service checks this against its cache (110C), they are the     same and so returns the cached “view” to the client. The User     Request therefore follows ‘Route B’ (as shown by dotted line in     FIG. 1) to produce the Response.

Some time later the service receives a new request for another “view” of a logical resource:

-   a) The service requests the adapter CVN (130C) -   b) The adapter returns a CVN=125 -   c) The service checks this against its cache (110C), they are     different and so the service then submits the relevant transactions     to the adapter so as to rebuild the “view” of the logical resource. -   d) The adapter returns the transaction data. The User Request     therefore follows ‘Route A’ (as shown by dashed line in FIG. 1) to     produce the Response.

At this stage, the cache is now possibly incoherent, and in the idle loop the contents can be updated.

It will be understood that the system as described above in relation to FIG. 1 is well known and need not be described in further detail. It will also be understood that the cache invalidation technique required to cope with possible incoherence of the cache is well known and also need not be described further.

Referring now also to FIG. 2, a write-through cache with two phase commit technique is used for logical configuration cache update.

When the user submits a configuration change transaction, the details of the request are constructed and are built into a request in the form that the subsystem requires (step 210). At this time a delta (change data) is prepared for the cache and is temporarily stored as a change pending for the logical resource cache (step 220)—this step constitutes phase 1 of the two-phase commit procedure.

The request is then sent to the subsystem for processing (step 230).

Upon receipt of the completed request the return code for the request is checked (step 240) (the return code may conveniently be an integer value that indicates either success or failure of a particular request—in the case of a failure the return code may be decoded into a failure reason):

-   a) if the request completed successfully the delta is applied to the     cache and the cache is now up to date with the contents of the     subsystem (step 260)—this constitutes phase 2 of the two-phase     commit procedure; -   b) if the request failed, the delta is destroyed (step 260) because     there is no need for it to be applied to the cache.

The transaction is then completed as normal (step 270).

It will be understood that the method of update of configuration cache data described above provides the advantage that known changes to the subsystem do not require an invalidate/rebuild style operation on the cache. This is especially important in the cache outlined above, where a change will invalidate the entire cache.

It will be appreciated that the method described above for update of configuration cache data will typically be carried out in software running on a processor (not shown), and that the software may be provided as a computer program element carried on any suitable data carrier (also not shown) such as a magnetic or optical computer disc.

It will also be appreciated that various modifications to the embodiment described above will be apparent to a person of ordinary skill in the art. 

1. In a system comprising a host coupled to a storage subsystem, a method for operating a write-through cache with a two phase commit technique for logical configuration cache update, comprising: during phase one, and in response to a submission of a configuration change transaction, constructing a request; and preparing change data for the cache and storing the prepared change data as a change pending for the cache; sending the request for processing; upon receipt of the completed request, checking a return code to determine success or failure of the request; and if the request completed successfully, the change data is applied to the cache for updating the cache with the contents of the storage subsystem, thereby executing phase two of the two-phase commit procedure; else if the request failed, the change data is deleted without being applied to the cache.
 2. In a system comprising a host coupled to a storage subsystem, the host comprising a write-through cache, said host further comprising a programmed data processor for operating the write-through cache with a two phase commit technique for logical configuration cache update, said data processor operating during a first phase, in response to a submission of a configuration change transaction, for constructing a request and for preparing and storing change data for the cache as a change pending for the cache; said data processor sending the request for processing and, responsive to a receipt of a completed request, checking a return code to determine success or failure of the request; said data processor being responsive to a condition where the request completed successfully for applying the change data to the cache for updating the cache with the contents of the storage subsystem, thereby executing phase two of the two-phase commit procedure; else said data processor is responsive to said request failing for deleting the change data without applying the change data to the to the cache.
 3. The host of claim 2, where said host is coupled to said storage subsystem through an adapter.
 4. An apparatus for updating of cache data in a storage system, the apparatus comprising: a memory for storing data; a cache for storing data associated with the memory; at least one processor for preparing change data for updating the cache, the at least one processor comprising circuitry for during phase one, and in response to a submission of a configuration change transaction, constructing a request for change to the memory; and preparing change data for the cache and storing the prepared change data as a change pending for the cache; sending the request for processing; upon receipt of a signal from the memory representative of completion of the request for change, checking a return code to determine success or failure of the request; and if the request completed successfully, the change data is applied to the cache for updating the cache with the contents of the storage subsystem, thereby executing phase two of the two-phase commit procedure; else if the request failed, the change data is deleted without being applied to the cache.
 5. The apparatus of claim 4, wherein the storage system comprises a disk storage subsystem.
 6. The apparatus of claim 5, wherein the memory is comprised in a disk adapter.
 7. The apparatus of claim 5, wherein the memory is comprised in a disk controller.
 8. A computer program storage device readable by a machine and comprising executable computer program instructions for updating of a cache in a storage system, the storage system comprising a memory holding data and a cache holding data associated with the memory, the instructions for performing the method of: during phase one, and in response to a submission of a configuration change transaction, constructing a request; and preparing change data for the cache and storing the prepared change data as a change pending for the cache; sending the request for processing; upon receipt of the completed request, checking a return code to determine success or failure of the request; and if the request completed successfully, the change data is applied to the cache for updating the cache with the contents of the storage subsystem, thereby executing phase two of the two-phase commit procedure; else if the request failed, the change data is deleted without being applied to the cache. 